DISC-CRANK.
305
dimensions of the three cylinder pairs in the chain ( The extension of our results to other cases will then be quite easy. Each of the four links of the slider-crank chain (C'gP- 1 -) Fig. 231 is more or less closely connected with its three cylinder pairs 1, 2, and 3, and their forms are therefore dependent upon the
relative sizes of the latter, although, as we have said, the nature of their motion is not affected by the same cause. Evidently, for instance, we do not alter the chain kinematically if we give to the full cylinder, or pin 1, on which the crank a revolves, a diameter so large that the profile of the pin 2 falls within it. Such an enlarge- ment, we shall call it an expansion,* of the pin is shown in Fig.
232. The open cylinder of d must now obviously be enlarged to exactly the same extent, so that the pair may still be closed. This arrangement, which may be shortly described as " 2 within 1," occurs in practice in some slotting and shearing machines, and in other cases when a short crank forms one piece with its own shaft.t
- Compare the idea of expansion with that of equidistant profiles in 35.
t It is a very common arrangement too for working a pump, on board ship or elsewhere, from the end of the crank-si) aft.
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